Xuxiang Li

Seasonal Variations and Evidence for the Effectiveness of Pollution Controls on Water-Soluble Inorganic Species in Total Suspended Particulates and Fine Particulate Matter from Xi'an, China

Abstract Total suspended particulate (TSP) and particulate matter less than 2.5 μm in aerodynamic diameter (PM2.5) sam ples were collected over Xi’an for a 1-yr period to characterize the seasonal variations of water-soluble inorganic ions and to evaluate the effectiveness of the pollution policies and controls during the past 10 yr. Mass concentrations of five cations (sodium [Na+], potassium [K+], ammonium [NH4 +]], calcium [Ca2+], and magnesium [Mg2+) and four anions (fluoride [F−], chloride [Cl−], nitrate [NO3 −], and sulfate [SO4 2−]) were determined by ion chromatography. The yearly arithmetic-mean mass concentrations of the total measured water-soluble ions in TSP and PM2.5 were 83.9 ± 58.4 and 45 ± 34.3 μg∙m-3. The most abundant ions in TSP were SO4 2−, NO3 −, Ca2+, and NH4 +; whereas in PM2.5 the dominant ions were SO4 2−, NH4 +, and NO3 −. Most of the ions were more concentrated in the PM2.5 than in TSP, but two exceptions were Ca2+ and Mg2+. Comparisons of the molar ratios of Mg2+/Ca2+ in TSP indicated that fugitive dust was the main source for these two ions, and the influence of soil dust from outside of the city was most evident during dust storms. The mass concentrations of SO4 2−, NO3 −, NH4 +, and K+ in TSP were highest in winter and lowest in spring, but Ca2+ was much higher in spring than other seasons because of suspended mineral dust. In PM2.5, NO3 − and K+ also showed winter maxima, but SO4 2− and NH4 + were highest in summer. Calculations of ion equivalents showed that TSP samples were more alkaline than PM2.5, the latter being weakly acidic in winter and autumn. High sulfur and nitrogen oxidation ratios occurred in summer and autumn, and there was evidence for the formation of ammonium bisulfate in TSP, ammonium sulfate in PM2.5, and ammonium nitrate in both fractions. Comparisons with the results of prior studies indicate that pollution controls in Xi’an have reduced the levels of air pollution over the past 10 yr. The SO4 2− concentration during the heating season in 2006 was only about one-eighth of that in 1996, and NH4 + decreased to one-ninth of that in 1996. Seasonal variations in the NO3 −/SO4 2− ratio are different than the patterns observed 10 yr ago, suggesting that emission sources have changed, with those from motor vehicles becoming increasingly important.

CHARACTERISTICS OF CLAY MINERALS IN ASIAN DUST AND THEIR ENVIRONMENTAL SIGNIFICANCE

The objectives of this research were to characterise the clay minerals composition of soil-derived dust in Northern China and to set up a mineralogical signature to trace their origin. Mineral composition of aerosol particles was investigated at Aksu, Dunhuang, Yulin, Tongliao and Changwu during an intensive field campaign period of ACE-Asia. The results show that the kaolinite (K) to chlorite (C) ratio is sensitive to the regional origin of Asian dust. Western source areas (represented by Aksu) displayed the lowest K/C ratio of 0.3 (average), while it was found to increase up to 0.70 (average) upon moving towards northern source areas (represented by Yulin). By studying transported dust in a deposition area representative of the Chinese Loess Plateau, the usefulness of the K/C ratio, when associated with back air-mass trajectories, was found to lie in revealing the origin of the dust. Comparison of the mineralogical data between Asian dust and Sahara dust, shows that the K/C ratio is also an effective signature to identify the source areas on a hemisphere scale.

Physiochemical characteristics of indoor PM2.5 with combustion of dried yak dung as biofuel in Tibetan Plateau, China

People inhabiting the Tibetan Plateau rely for survival on the yak, the regions native cattle. One of the important products of yak is dung, which has been served as cooking and heating fuels in the traditional Tibetan pastoralist society for several thousand years. The indoor air quality (IAQ) at eight residential homes with altitudes ranging from 3212 m to 4788 m was investigated in November 2012 to obtain a shot-term profile of emission from combustion of dried yak dung as biofuel in pastoral and agro-pastoral regions on the Tibetan Plateau. The indoor temperature, relative humidity, CO2 and mass concentrations of PM2.5 were monitored for around a 4-h period (5 kg dried fuel was consumed) at each site. Filter-based aerosol samples were also collected to characterize their elemental compositions, water-soluble ions, carbonaceous species and individual particle morphologies. The results showed that combustion of solid biomass fuel in cast-iron stove is the preliminary source of indoor particulate pollution. The average indoor and outdoor PM2.5 mass concentrations were 330.7 and 29.1 μg/m3, respectively. Individual particle analysis showed that most of the particles in smoke from dung burning were in the submicrometer size range. Regular and irregular organic balls and soot aggregates were the predominant species in the smoke (>90% in numbers). The data set in this study can provide significant basis for IAQ and epidemiology study on the Tibetan Plateau.

Study on the Progress of Ecological Fragility Assessment in China

The basic elements of human survival are based on the ecological environment. The development of social economic and the security of the ecological environment are closely linked and interact with each other. The fragility of the environment directly affects the stability of the regional ecosystem and the sustainable development of the ecological environment. As part of the division of the national ecological security, the assessment of ecological fragility has become a hot and difficult issue in environmental research, and researchers at home and abroad have systematically studied the causes and states of ecological fragility. The assessment of regional ecological fragility is a qualitative and quantitative analysis of the unbalanced distribution of ecological environment factors caused by human socio-economic activities or changes in ecosystems. At present, researches on ecological fragility has not formed a complete and unified index assessment system, and the unity of the assessment model has a direct impact on the accuracy of the index weights. Therefore, the discussion on selection of ecological fragility indexes and the improvement of ecological fragility assessment model is necessary, which is good for the improvement of ecological fragility assessment system in China.

Review of Land Use and Land Cover Change research progress

Land Use and Land Cover Change (LUCC) can reflect the pattern of human land use in a region, and plays an important role in space soil and water conservation. The study on the change of land use patterns in the world is of great significance to cope with global climate change and sustainable development. This paper reviews the main research progress of LUCC at home and abroad, and suggests that land use change has been shifted from land use planning and management to land use change impact and driving factors. The development of remote sensing technology provides the basis and data for LUCC with dynamic monitoring and quantitative analysis. However, there is no uniform standard for land use classification at present, which brings a lot of inconvenience to the collection and analysis of land cover data. Globeland30 is an important milestone contribution to the study of international LUCC system. More attention should be paid to the accuracy and results contrasting test of land use classification obtained by remote sensing technology.